Update user classification counts filtering by project if session time is false. do not return session time as key in response

[yuenmichelle1]

Small bug found:
eg.
https://eras-staging.zooniverse.org/classifications/users/1234?start_date=2022-03-10&project_id=1974&period=day

returns

{
    "total_count": 24,
    "data": [
        {
            "period": "2022-09-09T00:00:00.000Z",
            "count": 23,
            "session_time": null
        },
        {
            "period": "2022-09-20T00:00:00.000Z",
            "count": 1,
            "session_time": null
        }
    ]
}

This PR makes sure session_time is not a key in response data when time_spent=true